[src/trunk]: src/lib/libossaudio ossaudio(3): Clone some useful behaviour fro...

[nia <nia%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/b3256812eb7c
branches:  trunk
changeset: 946003:b3256812eb7c
user:      nia <nia%NetBSD.org@localhost>
date:      Fri Nov 13 09:02:39 2020 +0000

description:
ossaudio(3): Clone some useful behaviour from the Solaris kernel

Both SNDCTL_DSP_SPEED and SNDCTL_DSP_CHANNELS support a special value
0 to "query the configured value without changing it". In our case,
this actually means setting and querying the hardware rate.

I don't know if OSSv3 or FreeBSD or other implementations also do this.
But it seems safe and sensible to support.

diffstat:

 lib/libossaudio/ossaudio.c |  27 ++++++++++++++++++++++++---
 1 files changed, 24 insertions(+), 3 deletions(-)

diffs (55 lines):

diff -r 084eb4f93c4e -r b3256812eb7c lib/libossaudio/ossaudio.c
--- a/lib/libossaudio/ossaudio.c        Fri Nov 13 09:01:59 2020 +0000
+++ b/lib/libossaudio/ossaudio.c        Fri Nov 13 09:02:39 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: ossaudio.c,v 1.63 2020/11/04 22:59:24 nia Exp $        */
+/*     $NetBSD: ossaudio.c,v 1.64 2020/11/13 09:02:39 nia Exp $        */
 
 /*-
  * Copyright (c) 1997, 2020 The NetBSD Foundation, Inc.
@@ -27,7 +27,7 @@
  */
 
 #include <sys/cdefs.h>
-__RCSID("$NetBSD: ossaudio.c,v 1.63 2020/11/04 22:59:24 nia Exp $");
+__RCSID("$NetBSD: ossaudio.c,v 1.64 2020/11/13 09:02:39 nia Exp $");
 
 /*
  * This is an Open Sound System compatibility layer, which provides
@@ -184,7 +184,26 @@
                break;
        case SNDCTL_DSP_SPEED:
                AUDIO_INITINFO(&tmpinfo);
-               /* Conform to kernel limits. */
+               /*
+                * In Solaris, 0 is used a special value to query the
+                * current rate. This seems useful to support.
+                */
+               if (INTARG == 0) {
+                       retval = ioctl(fd, AUDIO_GETBUFINFO, &tmpinfo);
+                       if (retval < 0)
+                               return retval;
+                       retval = ioctl(fd, AUDIO_GETFORMAT, &hwfmt);
+                       if (retval < 0)
+                               return retval;
+                       INTARG = (tmpinfo.mode == AUMODE_RECORD) ?
+                           hwfmt.record.sample_rate :
+                           hwfmt.play.sample_rate;
+               }
+               /*
+                * Conform to kernel limits.
+                * NetBSD will reject unsupported sample rates, but OSS
+                * applications need to be able to negotiate a supported one.
+                */
                if (INTARG < 1000)
                        INTARG = 1000;
                if (INTARG > 192000)
@@ -1708,6 +1727,8 @@
  * case an application is abusing SNDCTL_DSP_CHANNELS - OSSv4 always sets and
  * returns a reasonable value, even if it wasn't what the user requested.
  *
+ * Solaris guarantees this behaviour if nchannels = 0.
+ *
  * XXX: If a device is opened for both playback and recording, and supports
  * fewer channels for recording than playback, applications that do both will
  * behave very strangely. OSS doesn't allow for reporting separate channel